A power module is used for an electronic apparatus which needs a switching for large current, such as in-vehicle equipment or industrial equipment. In the power module, an insulated substrate on which a circuit is formed, and a heat radiation substrate equipped by contacting a heat sink, are jointed with solder. In the electronic apparatus, a heat is conducted from the insulated substrate to the heat radiation substrate via a solder layer for the solder joint, and radiated to the heat sink.
However, with usage of the electronic apparatus, an external force such as vibration is added to the electronic apparatus, and a heat is generated at devices in the electronic apparatus. By the external force or a heat load of the heat generation, a failure such as a crack occurs at the solder layer By this failure occurred at the solder layer, a radiation performance of the electronic apparatus often falls. Accordingly, in order to maintain the radiation performance and safety of the electronic apparatus, reliability of solder joint between the insulated substrate and the heat radiation substrate is desirable to be raised.